Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-12-08
2003-08-26
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S111000, C522S153000, C522S156000, C264S485000, C264S488000
Reexamination Certificate
active
06610761
ABSTRACT:
TECHNICAL FIELD
The present invention relates to ionizing radiation irradiated rubber molded product and to a process for preparing the same.
BACKGROUND ART
Acrylic rubbers have higher heat resistance and oil resistance than conventional general-purpose rubbers and are in use for various kinds of industrial seal materials.
However, the acrylic rubbers are not fully satisfactory in compression set and heat resistance at temperatures not lower than 150° C. and are unusable for seal materials, hoses and electrical wires at such temperatures.
On the other hand, fluororubbers are excellent in heat resistance, compression set, oil resistance and resistance to chemicals and are useful in the field of industrial materials and other fields. Nevertheless, it appears unlikely that the fluororubbers will be used in remarkably increased quantities in spite of their outstanding properties since economy is not negligible for prevalent use in these fields. Additionally, fluororubbers have the drawback of deteriorating in the presence of additives (especially amine compounds) contained in engine oils.
Investigations were conducted to develop materials having the characteristics of both acrylic rubbers and fluororubbers by blending a common acrylic rubber with a common fluororubber and vulcanizing the blend for molding with use of vulcanizers for one or both of the rubbers, whereas the method failed to fully vulcanize one or both of the rubbers, giving products which were unsatisfactory in physical properties such as mechanical strength and compression set, heat resistance, and other properties.
Materials have been developed which render a fluororubber and an acrylic rubber peroxide-cocrosslinkable to overcome the foregoing drawbacks (WO 96/17890). Yet, products unsatisfactory in mechanical strength were obtained by crosslinking methods using conventional crosslinking agents.
An object of the present invention is to provide an ionizing radiation irradiated rubber molded product which is excellent in heat resistance, compression set, oil resistance, resistance to chemicals and resistance to additives and which is improved in mechanical strength.
DISCLOSURE OF THE INVENTION
The present invention provides an ionizing radiation irradiated rubber molded product as described below and a process for preparing the same.
The ionizing radiation irradiated rubber molded product of the present invention is prepared by irradiating with an ionizing radiation a preform comprising 5 to 95% by weight of a fluororubber containing vinylidene fluoride copolymerized therein in a proportion of 45 to 88 mole % and having a number average molecular weight of 5,000 to 200,000, and 95 to 5% by weight of an acrylic rubber.
Stated more specifically, the rubber molded product of the invention is prepared by preforming the following rubber composition, and irradiating the preform with an ionizing radiation.
According to the rubber molded product of the invention, examples of fluororubbers are vinylidene fluoride copolymers such as vinylidene fluoride/hexafluoropropylene, vinylidene fluoride/ tetrafluoroethylene/hexafluoropropylene and vinyl idene fluoride/chlorotrifluoroethylene; copolymers such as tetrafluoroethylene/propylene, hexafluoropropylene/ethylene and fluoro(alkyl vinyl ether)/olefin (for example, vinylidene fluoride/tetrafluoroethylene/perfluoroalkyl vinyl ether), etc. Preferable among these are elastomers of vinylidene fluoride/hexafluoropropylene and vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene. The fluoro(alkyl vinyl ether) may contain a plurality of ether linkages. These fluororubbers are 5,000 to 200,000, preferably 50,000 to 170,000, in molecular weight, i.e., in number average molecular weight. The fluororubber fails to give satisfactory processability if exceeding 200,000 in molecular weight, while fully acceptable characteristics are unavailable after vulcanization if the molecular weight is lower than 50,000. The term processability means the vulcanization characteristics and amenability to rolling process and mold process. The proportion of copolymerized vinylidene fluoride in the fluororubber is 45 to 88 mole %, preferably 55 to 85 mole %.
The fluororubber is low in compatibility with acrylic rubbers and encounters difficulty in giving higher dispersibility to polymers and sufficient mechanical property is not obtained if less than 45 mole % in the proportion of copolymerized vinylidene fluoride. Impaired compression set will result if this proportion exceeds 88 mole %.
The peroxide-crosslinkable fluororubber has a crosslinking moiety in the molecule, such as iodine, bromine, double bond or the like which moiety will undergo crosslinking reaction in the presence of a peroxide radical.
The fluororubbers of the invention include, for example, iodine-containing fluororubbers, which will be described below.
The preferred examples of iodine-containing fluororubbers include a readily curable fluororubber (see JP-A-125491/1978) which is obtained by polymerizing vinylidene fluoride (VdF) and at least one of monomers comprising a fluorine-containing ethylenically unsaturated compound having 2 to 8 carbon atoms (and when required, a fluorine-free ethylenically unsaturated compound having 2 to 4 carbon atoms) in the presence of a radical generator and an iodine compound represented by the formula RIx (wherein R is a saturated or unsaturated fluorohydrocarbon group having 1 to 16 carbon atoms, chlorofluorohydrocarbon group or hydrocarbon group having 1 to 3 carbon atoms, and x, which is the number of bonds of R, is an integer of not smaller than 1). Useful iodine-containing fluororubbers are copolymers containing 45 to 88 mole %, preferably 55 to 85 mole %, of vinylidene fluoride (VdF) unit, 0 to 45 mole %, preferably 0 to 30 mole %, of tetrafluoroethylene (TFE) unit and 10 to 40 mole %, preferably 10 to 25 mole %, of hexafluoropropylene (HFP) unit.
The acrylic rubber for use in preparing the ionizing radiation irradiated rubber molded product of the present invention is preferably a multi-polymer rubber comprising (a) 30 to 99.9% by weight of (meth)acrylic alkyl ester and/or (meth)acrylic alkoxy-substituted alkyl ester, (b) 0.1 to 10% by weight of a crosslinkable monomer and (c) 0 to 70% by weight of other ethylenically unsaturated compound copolymerizable with the components (a) and (b).
Examples of the above (meth)acrylic alkyl ester to be used herein are, for example, compounds represented by the formula
CH
2
=C(R
1
)COOR
2
wherein R
1
is a hydrogen atom or methyl, and R
2
is alkyl having 1 to 18 carbon atoms. Examples of such monomers are methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-methylpentyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate and n-octadecyl (meth)acrylate. Among them, preferable are methyl acrylate, ethyl acrylate, n-propyl acrylate and n-butyl acrylate, and more preferable are methyl acrylate and ethyl acrylate.
Examples of the above (meth)acrylic alkoxy-substituted alkyl ester are compounds represented by the formula
CH
2
=(R
1
)COO-A-O-R
3
wherein A is alkylene having 1 to 12 carbon atoms, R
1
is as defined above and R
3
is alkyl having 1 to 12 carbon atoms. Examples of such compounds are 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(n-propoxy)ethyl (meth)acrylate, 2-(n-butoxy)ethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 2-(n-propoxy)propyl (meth)acrylate and 2-(n-butoxy)propyl (meth)acrylate. Among them, preferred are 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate, and more preferred is 2-methoxyethyl acrylate.
Examples of the above crosslinkable monomer are dicyclopentadiene, ethylidenenorbornene, vinyl chloroacetate, allyl chloroacetate, 2-chloroethyl vinyl ether, vinyl (meth)acrylate, allyl (meth)acrylate, glycidyl (meth)acrylate, dimethyl stearyl vinylsilane, dicyclopenteny
Matsumoto Kazuhisa
Shirai Yoshihiro
Berman Susan W.
Daikin Industries Ltd.
Kubovcik & Kubovcik
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